This invention relates to the cogeneration of electricity and liquid carbon dioxide (CO.sub.2) by the combustion of natural gas or like fuel gas rich in methane. More particularly, the invention achieves such cogeneration with a simple integrated system and with high efficiency relative to the thermal energy of the fuel gas consumed.
In recent years, the cogeneration of electricity and saleable refrigeration or steam has received intensified investigation. Many processes have been proposed and some have been commercially adopted. For example, U.S. Pat. No. 4,711,093 to Markbreiter and Dessanti discloses and claims a recent development in which pipeline gas is work-expanded to produce electricity and refrigeration. Other cogeneration systems have been built and are producing electricity and steam by burning methane-rich gas in a turbine.
However, it is not always practical at any given location where electricity is needed to find customers who are available to purchase steam or refrigeration.
The sales expansion or carbonated drinks such as beer and various sodas and frozen foods has led to a worrisome, tight supply of food-grade CO.sub.2. It is common practice that food-grade CO.sub.2 is transported as a liquid from the supplier to the plants producing carbonated beverages or frozen foods by tank truck. The dual circumstances that liquid CO.sub.2 is in short supply and is readily transported from its source to its consumption have, together with the need for a cogeneration process that yields electricity and a product other than refrigeration or steam, sparked the conception of this invention.
Accordingly, a principal object of the invention is to cogenerate electricity and liquid CO.sub.2 by the combustion of natural gas or like fuel gas.
Another important object is to provide a simple, integrated cogeneration system in which all of the power required by the system is derived from the combustion of the fuel gas.
A further noteworthy object is to operate the cogeneration system with high efficiency relative to the thermal energy of the fuel gas which is burned.
These and other objects and advantages of the invention will be evident from the description which follows.